1. Field of the Invention
The present invention generally relates to computer networks, and, more specifically, to a method and system for routing communication traffic over primary and backup communication channels. In one embodiment the primary channel comprises a free-space optical (FSO) communications systems link
2. Background Information
With the increasing popularity of wide area networks (WANs), such as the Internet and/or the World Wide Web, network growth and traffic has exploded in recent years. Network users continue to demand faster networks and more access for both businesses and consumers. As network demands continue to increase, existing network infrastructures and technologies are reaching their limits.
An alternative to present day hardwired or fiber network solutions is the use of wireless optical communications. Wireless optical communications utilize point-to-point communications through free-space and therefore do not require the routing of cables or fibers between locations. Wireless optical communications are also known as free-space optical (FSO) or atmospheric optical communications. In a typical free-space optical communication system, a modulated beam of light is directed through free-space from a transmitter at a first location to a receiver at a second location. Data or information is encoded into the beam of light by means of the modulation. Once received by the receiver, the modulated beam of light is demodulated and corresponding data and information may then be extracted. This scheme enables data and information to be transmitted through free-space from the first location to the second location.
Transmission of optical signals through free space poses many challenges. Since the atmosphere is the propagation medium for FSO transmissions, various weather conditions, such as fog, can greatly degrade signal strength and link distances. In some instances, the conditions are such that the use of an optical link is temporarily unavailable. Under these conditions, it is common to switch to a backup “land-line” network link, such as a T1 telecommunications link, to maintain the communication channel. Generally, the backup link will only provide a fraction of the bandwidth available with the optical link. As a result, it is desired to use the primary (optical) link whenever possible. However, it is also very important that data losses be kept to a minimum.
In a typical FSO system, a distribution switch or the like is used to reroute communication traffic to a backup link when routing via an optical link is not possible. Conventionally, this may be done by monitoring handshaking signals, such as Open Shortest Path First (OSPF) “hello” packets, or monitoring other optical link performance characteristics, such as dropped packets. For example, when an insufficient number of “hello” packets are received, the distribution switch may reroute the communication traffic to the backup link. In some instances, the optical link may enter a marginal operating state. In this state, a sufficient number of “hello” packets may be received to keep a route active, but high link-error rates and their resulting re-transmission of data packets significantly degrades link bandwidth for customer data. This situation may lead to network “flapping,” which describes a condition in which the optical link goes in and out of tolerance and the distribution switch and other network devices used for routing traffic have to excessively reconfigure their routing tables in response to each routing switch to maintain the communications link. This may lead to a large percentage of the network bandwidth being unavailable for the communication traffic.